Contribution of Li substitution for Zn to green light emission of ZnO ceramic thin films

In this paper, lithium-doped ZnO films were precipitated on n-type Si (100) substrates by the sol-gel method. The crystal structure, surface morphology, and luminescence properties of the lithium-doped ZnO films were investigated. The results of the X-ray diffractometer (XRD) measurements show that the ZnO thin films with different lithium doping concentrations all have an obvious preferred orientation. According to the fitting result of photoluminescence (PL) spectra, we identify the existence of Li substitution for Zn acceptor defects and that the green emission peaks are caused by the dual effects of single ionized oxygen vacancy (VO•) to the valence band top and VO• to Li substitution for Zn acceptor transitions. From the PL spectra, no matter the number of spin-coated layers, there is a corresponding lithium doping ratio, which can make the Li substitution for Zn acceptor defects concentration reach saturation. Under the same spin-coated layer, the visible luminescence intensity is significantly enhanced with an increase in lithium doping concentration. When the doping concentration reaches a certain value, the luminescence intensity reaches its maximum. Due to concentration quenching, a higher lithium doping ratio will result in a decrease in luminescence intensity.